There are many types of monitoring systems wherein each monitoring system monitors conditions in remote areas from a central location. The need for such systems is readily recognizable. A remote area, occasionally referred to as a zone or a sector, frequently corresponds to an apartment or a room wherein a condition is monitored. Smoke detectors and intrusion detectors are common types of detectors used to monitor conditions within remote areas. Various methods have been utilized to provide a central location with limited amounts of information corresponding to the monitored conditions.
Most monitoring systems which monitor conditions in remote areas from central locations have the ability to at least determine that some type of condition has changed from a normal state to an off-normal state somewhere within the monitored areas. One of the simplest methods for accomplishing this is a single current loop with detectors placed in a series electrical relationship with each other proceeding from the central location through each area and back to the central location. As long as current flows through a normally closed loop, or as long as no current flows in the alternate normally open loop, it is often assumed that no monitored condition has changed. It should be evident that this type of system has its limitations, including the inability to determine the area in which a detection or combination of detections occurs, the inability to determine which detector or combination of detectors senses a condition change or combination of condition changes, and the inability to distinguish a break in the current loop due to a fault in the line from an actual detection or combination of detections.
In an effort to at least solve these problems, a method was developed which is described in U.S. patent application Ser. No. 07/322,166 filed on Mar. 13, 1989, allowed Jun. 18, 1990, which is a continuation of U.S. patent application Ser. No. 07/129,158 filed on Dec. 7, 1987. This method solves the problem of determining in which area a detection or combination of detections occurs by connecting each remote area to the central location with separate and distinct communication links. Although this method solves this problem, cost often becomes a significant factor when providing separate wires to a large number of remote areas or to remote areas where the distance to the central location is very large. Secondly, this method solves the problem of determining which detector or combination of detectors senses a condition change by introducing unique impedances into the circuit which correspond to different types of detectors. Analog measurements are then made at the central location to identify the type of condition change or combination of changes detected. Although this method substantially solves the problem of determining which detector or combination of detectors senses a condition change or combination of condition changes, the size of the system becomes a significant factor. As the number of detectors and the number of remote areas grow, it can become increasingly difficult to distinguish which detector or combination of detectors is responsible for the change in impedance at the central location. Therefore, although this method solves the problems set forth above, additional problems frequently arise.
Others have attempted to overcome these and other problems through a method which avoids using separate communication links for each area by connecting remote areas together on a common link in a "bus" manner, a parallel interaction between remote areas. Each remote area then uses the same wire or set of wires to communicate with the central location. One method of communicating along a link of this type includes transmission of unique signals from each remote area to the central location upon detection of a condition change. An example of this method can be seen in U.S. Pat. No. 3,925,763. Each signal contains identification of the type of detection which occurred as well as the remote area in which it occurred. In an apparent effort to overcome potential interference between simultaneous signals from different remote areas, a line-activity sensing mechanism is used. One potential problem with this type of method of communication Is that one remote area may be required to wait an unacceptably long period of time before the line is clear, thus delaying a potentially very important signal. Another problem is related to the ability to determine when line faults occur. This method apparently does not inherently solve this problem without the need for additional signal generating and sensing devices.
Another method for using a continuous communications link between remote areas is a polling method. A polling method is a method by which a scanner device located in the central location polls receiver devices in the remote areas. The scanner transmits a polling signal which is received by all of the receivers, and only one receiver responds to the polling signal by transmitting a response back to the scanner. This method of polling over a continuous communications link inherently solves the problem of identifying a line fault while also providing at least partial solutions to the other problems relating to detector identification, remote area identification, and system cost and size considerations. This method also ensures that no interference between simultaneous signals from separate remote areas will occur.
One polling method includes continually pulsing the common communication link with pulses from the central location at a predetermined frequency to sequentially poll each remote area for responses. Examples of this method are seen in U.S. Pat. No. 3,927,404. Receiver devices within each remote area count the number of pulses and respond between pulses when the number of pulses reaches an assigned number. One disadvantage of this type of polling method is that regardless of the number of remote areas within a system, the number of pulses between two pollings of the same remote area is often the same, depending on the size of the counters in the receivers. In other words, if a counter which counts up to 2048 is used in a system using this method and including only 700 remote areas, the system is serving no function for 1348 cycles of polling pulses, valuable time is wasted. Another potential problem is the sequential loop into which the polling is apparently locked. It would appear to be impossible to address a particular receiver without polling through a requisite number of preceding receivers. Although polling is used in this method, other problems arise from the implementation of a single pulse/counter method of polling.
in general, two problems associated with a polling method arise when there is a need to cover every monitored condition throughout the system in a continuous manner. The first problem concerns the ability of the system to effectively cover every monitored condition. Two or more conditions may often be in off-normal states at the same time. One option of dealing with this problem is to ignore all detections which occur after a first detection. Because they are ignored, later detections which might be more important than the first detection may go unnoticed for an unacceptably long period of time, if not completely ignored. Another option is to utilize a priority method of distinguishing the most important detections and generating a response signal which represents the most important detection. An example of this method is also shown in U.S. Pat. No.
3,927,404. Although the most "important" detection may be communicated, other information is frequently very useful. For instance, if smoke is sensed in an apartment, an "important" detection, the ability to know that a door opened while the fire alarm was sounding, implying that the resident escaped the fire, is not part of a priority method. The priority method does not provide complete coverage of every monitored condition.
The second problem concerns the requirement of continuous coverage. Conditions frequently change from normal states, to off-normal states, and back to normal states very quickly. These momentary off-normal condition changes can be initiated and completed during the time between pollings of a particular receiver. If some type of memory element is not assigned to each possible detection, a detection could go unnoticed, thus the coverage would not be continuous. An example of this method is shown in U.S. Pat. No. 4,562,428. No memory devices are specifically assigned to each possible detection. Detectors which only emit a momentary indication of a change are not adequately accommodated by this type of a system. Although the polling rate may be high and the number of receivers may be low, reducing the likelihood of missing a momentary off-normal condition, the coverage is simply not continuous.
Another problem related to monitoring systems concerns power supply methods. One method of supplying power to remote areas requires that remote power from each remote area be supplied to the detectors. Because one or more remote areas may lose power at any given time, a system which requires that each remote area be remotely powered is, in many cases where continuous coverage is necessary, unacceptably unreliable. Conversely, other types of monitoring systems require that power be supplied to each remote area from the central location and are not equipped to receive power from each remote area. Those types of systems do not adequately accommodate environments requiring cable-less links between the central location and remote areas. Such environments may require that each remote area be powered remotely. Therefore, many monitoring systems are either unacceptably unreliable due to a system-imposed requirement that power be supplied at each remote area or are incapable of accommodating environments requiring cable-less links between the central location and the remote areas because power must be supplied to each remote area from the central location.
Another problem related to monitoring systems concerns the difficulty of providing adequate protection to people residing in the so-called remote areas while providing an appropriate degree of freedom to those people. One example of an environment in which a monitoring system of this type might be utilized is that of a high rise residence building for elderly people. One example of a monitoring system which would commonly be used in this environment is the standard "nurse call" system used in many hospitals and nursing homes. That type system often requires that an elderly person in need of assistance physically move to a call button or pull-chain to alert care personnel of a medical emergency. Depending on the type of emergency, this requirement is often impossible. Some systems have overcome that problem by equipping each monitored person with a personal radio transmitter located in a pendant or wrist-watch which communicates with a radio receiver located in the monitored person's room. Each transmitter is typically coded to only communicate with one particular radio receiver and frequently has a very limited range. Because of these limitations, the monitored person, in order to maintain constant protection, is either restricted to his/her room or must be continually accompanied by care personnel when outside his/her room. Hence, those systems do not, by simple virtue of carrying a pendent transmitter, give a monitored person the ability to roam throughout the complex with continuous protection. This is a severe limitation on the monitored person's freedom to move about and is arguably too high a price for continuous protection.